A:①③
B:①④
C:②③
D:②④
函数y=sinπ3x在区间0,t上至少取得2个最大值,则正整数t的最小值是( )
I think July is ____ (hot) than any other month in our country. It's ____ (hot) month of the year.
Jack, American teacher,is arriving at our school by car.
如图所示,自行车传动装置由前后大小齿轮及链条组成,A、B为大小齿轮边缘上的两点,A、B两点的角速度分别为ωA和ωB,线速度大小分别为vA和vB,则( )